The field of this invention relates generally to video cameras, and more specifically, to an endoscopic video camera head configured to shield the imager and imager electronics from electro-magnetic interference, to electrically isolate the head from the patient, and to be sterilizable using the steam autoclave process.
In the recent past, the need for small, lightweight video cameras using a solid state image sensor ("imager") such as a charge coupled device ("CCD"), charge injection device ("CID"), or metal oxide semiconductor ("MOS") has rapidly developed for both medical and industrial applications. One medical application involves a video camera attached to an endoscope to allow observation of a surgical site, an internal body structure, or an organ. With a diameter of from 5 to 10 mm., endoscopes are passed into body cavities through small holes to observe structures and perform procedures previously requiring large surgical openings.
In this arrangement, the imager may be contained in a small camera head and attached to the endoscope eyepiece so that the camera head/endoscope combination, or video-endoscope, is lightweight and easily manipulable by a surgeon. A flexible cable connects the camera head to the rest of the camera electronics which are usually included in a camera control unit located remotely from the camera head, and connected via a cable. The camera control unit includes control and video processing circuitry which sends operating signals to the imager and receives signals from the imager which are processed for video display. The camera control unit is also coupled to a video monitor for viewing of the surgical site by one or more physicians. The smallest cameras are made with a single imager but other multiple-imager cameras are also in use, as described in U.S. Pat. No. 5,428,386, which is hereby fully incorporated by reference herein as though set forth in full.
An industrial application employing an imager involves observation of industrial processes in which direct observation by a person is unsafe or otherwise impractical. Such processes include those occurring in nuclear power generating stations, furnaces or engine compartments, or other processes which are generally inaccessible. Here, a camera head including an imager may be attached to a hole in the wall of the vessel in which the process occurs. The camera head is then connected by cable to a camera control unit and video monitor at a remote location in similar fashion to that described above.
Additional background and details regarding video cameras, and their use in medical endoscopic applications, are provided in the following co-pending applications, each of which is assigned to Envision Medical Systems, Inc., and each of which is hereby incorporated by reference herein as though set forth in full:
______________________________________ Ser. No. Filing Date Title ______________________________________ 08/393,284 February 23, 1995 REMOTE IMAGER U.S. Pat. No. VIDEO CAMERA 5,696,553 CABLE COMPENSATION CIRCUITRY 08/458,437 June 2, 1995 FIBERSCOPE ENHANCEMENT SYSTEM 08/589,875 January 23, 1996 REMOTE CCD VIDEO CAMERA WITH NON- VOLATILE DIGITAL MEMORY 08/018,053 February 16, 1993 STERILIZABLE CCD VIDEO CAMERA ______________________________________
A critical design goal of an endoscopic CCD video camera is electrical safety, both from the standpoint of the operator, and from the standpoint of the patient. Of particular relevance in this regard is the newly adopted safety requirements and regulations of the unified European Community (EC)--the International Electrotechnical Commission, Medical Equipment Particular Standards for Safety of Endoscopic Equipment (IEC 601-2-18)--which are not only becoming common for all Europe, but are finding acceptance world-wide, including within testing agencies in the United States such as the Underwriters Laboratories (UL) standard UL2601. One specific aspect of these safety regulations states that endoscopic equipment that contacts the patient, and in some cases the operator, must be electrically isolated from ground and power sources.
A problem thus arises because most endoscopic video cameras include a grounded metal housing to (1) protect the sensitive CCD imager and associated electronics from susceptibility to externally generated electro-magnetic interference (EMI) and (2) control emissions of electro-magnetic energy generated internally by the camera head circuitry. The need to achieve acceptable electro-magnetic compatibility (EMC), that is, to control electro-magnetic susceptibility and emissions, is quite important. This is especially true in the surgical setting in which there often exists both strong sources of EMI such as electrocautery units and sensitive instruments such as oxygen and CO.sub.2 monitors. Moreover, permissible electro-magnetic emission levels are now specified by domestic and international regulation in the same way as other safety standards. In Europe, pursuant to International Electrotechnical Commission IEC 601-1-2, the governing standards are defined by CISPR 11, IEC 801-2, IEC 801-3, IEC 801-4, and IEC 801-5; in the United States, the Food and Drug Administration (FDA) has set forth the applicable standard in MDS 201-0004; and in the United European community (EU), according to an EMC Directive, the governing standards are essentially a composite of the above. In current endoscopic video cameras, this metal housing can easily contact the patient or operator, thus interfering with the objective of achieving compliance with applicable domestic and international safety standards.
Another problem is the difficulty of isolating the patient or user from the power sources used to drive the imager electronics and the camera control unit. Attempts to isolate the camera head from the endoscope by constructing the endoscope eyepiece from a non-metallic material have not proven successful because the limited isolation provided thereby has been easily bridged by the operator's wet hand.
Moreover, there is a growing practice amongst physicians to view images produced by an endoscope on a television monitor, in contrast to viewing these images directly through the endoscope eyepiece. As surgeons have become more comfortable with this practice, the need for the endoscope and imager to be separable at the eyepiece has decreased. This development has permitted the acceptance of one piece video-endoscopes in which the camera head and endoscope are screwed together or permanently joined, thus allowing for fewer glass interfaces, fewer potential liquid leak paths, and better overall performance. Such a design eliminates the eyepiece, and with it any possible isolation available therefrom by creating a direct connection between the metal endoscope and the metal camera head housing.
Further, known attempts to achieve electrical isolation has not proven successful. For example, Kikuchi, U.S. Pat. No. 4,931,867, describes an approach in which the camera control electronics are segregated into a camera input circuit and a camera output circuit which are isolated from one another through isolation circuitry. This approach is not satisfactory because it allows the camera input circuit and cable shield to float relative to the camera output circuit and video output. Consequently, the potential between this circuitry can become large and induce noise into the sensitive camera circuits. Moreover, electrical isolation between the patient and the metal enclosure of the camera head is not achieved.
Another critical design goal of an endoscopic CCD video camera is sterilizability. Because the camera head and cable are used within the sterile field (an arbitrary area around the surgical site) they must be disinfected like other surgical instruments. The steam autoclave method has long been the preferred method for sterilization, especially for instruments that can withstand the necessary high temperature, 134.degree. C., and the extreme conditions associated with steam sterilization. In the past, instruments such as endoscopic cameras were not thought as being able to withstand the steam autoclave process. Accordingly, these instruments were either treated by less effective means such as cold soak processes or moderate temperature (55.degree. C.) processes, or the camera head and cable were covered with a sterile disposable plastic cover during surgery. Each of these methods has significant disadvantages when compared with the steam autoclave method. For example, the cold soak processes do not achieve the same level of sterility, and the moderate temperature processes involve longer cycle times (2 hours) and the handling and disposal of highly toxic chemicals.
Recently, short exposure steam sterilization techniques have been developed to sterilize instruments more rapidly. One such method, known as flash sterilization, reduces the usual steam autoclave time of 45 minutes to less than 10 minutes by using vacuum evacuation of the steam chamber and elimination of the cloth wrapping procedure that protects the sterilized instruments during storage. The appearance of increasingly virulent contaminates and the need to quickly prepare instruments between procedures has made flash steam sterilization the method of choice for many surgical instruments.
The problem is that many metallic instruments, such as current endoscopic instruments, are usually too hot for immediate use and thus must undergo a cooling-off period. A significant cooling-off period is inconsistent with the objective of efficiently utilizing surgical resources and minimizing equipment or instruments necessary to support an operating room schedule.
Moreover, known attempts to achieve rapid sterilization have not proven successful. For example, Henley, U.S. Pat. No. 5,010,876, describes an approach in which a disposable video camera is used to achieve improved sterility; Adair, U.S. Pat. No. 4,914,521, describes an approach in which a sterilizable video camera cover is applied over a camera to achieve sterile operating conditions; Watanabe, U.S. Pat. No. 4,756,304 describes an approach in which a sterile plastic camera housing is used to cover camera in order to achieve sterility; and Watanabe, U.S. Pat. No. 4,590,923 describes an approach in which a camera is inserted into a metal tubular sterilizable housing in order to achieve sterility. The problem with all these approaches is that they are either uneconomic, cumbersome, or interfere with the objective of achieving electrical isolation of the camera head.
Consequently, it is an object of the subject invention to provide a video camera head configured for use in an endoscopic video camera system which is adequately shielded from EMI and yet is electrically isolated from contact with a human or conductive fluids. Another objective is to provide a video camera head which is readily sterilizable through the steam autoclave process, and which minimizes the cooling-off period required after such a method is employed. Further objects of the invention include utilization of the above concepts alone or in combination. Additional advantages and objects will be set forth in the description which follows, or will be apparent to those of ordinary skill in the art who practice the invention.